Ask a man to describe a woman who’s a “10,” and statistically, the main criteria are not likely humor, manners and ambition. But for Lulu, the new social networking app that allows women to rank and review their male Facebook friends and former flings, those are the first three categories in an algorithm that gives men a score from 1-10. Appearance is last.

The concept of ranking a guy by a number may sound petty, but a 10 on Lulu is the whole package, because frankly, apart from casual hookups, that’s how women pick their suitors. Sexy is as sexy does.

Women and men alike are ranting that Levine is undeserving of his new title because frankly, he can come off as kind of a jerk. But others argue he’s undeniably, physically sexy—so what’s the big deal?

The problem is that the idea of sexy is a complicated concept for women who tend to be more qualitative, and less hierarchical when it comes to assessing guy’s attractiveness. Sure bad boys have always had appeal, but when someone is named the ultimate “sexiest” guy anywhere, lots of women feel that personality should be a part of the equation.

For example, if Joseph Gordon-Levitt, well known for his starring role in “500 Days of Summer,” were declared Sexiest Man Alive, would there be as much backlash? Probably not. He may not look like a model, but he’s charming and his sweet-guy public image suggests that he calls his mother on Sundays. Whereas Adam Levine told Women’s Health “Let’s face it, I only practice yoga because the classes are always packed with beautiful women.” He was joking, but still, those things matters in the way women assess men.

That kind of thinking is basic biological science. Research shows that when women are looking for a mate, they tend to be pickier since they bear the greater parental investment. And when it comes to the characteristics that people value in a mate, there are significant gender differences. When women asked to rate what characteristics are most important to them for a suitable partner, women are most likely to list: considerate, honest, understanding, loyal and interesting to talk to. Whereas men say they prefer women who are physically attractive, good looking, and frugal. It’s not that men are ultimately more shallow, but our checklists at first encounter are different.

Take Lulu’s recent popularity. The app, which has over 1 million users and about 2.5 million reviews, is solely for female users, who anonymously rank their male Facebook friends on criteria including, humor, manners, ambition, commitment and appearance. Using its algorithm, Lulu grants each guy a number from 1 to 10. But that’s not all. Women also select hashtags that best describe their former fling or friend—and they’re quite detailed and specific like “#DoesDishes” and “#GoneByMorning.”

The results are a pretty accurate—I was surprised to see how well my own friends and former boyfriends were characterized. And interestingly, Lulu founder Alexandra Chong told me that 70-80% of users’ reviews focus on personality traits over physical features.

“It’s about validating your experiences and that’s rewarding. As women, we have the need to share, and we are far more communicative than men,” says Chong.

Chong says Lulu isn’t a dating application—they plan to have a review platform for beauty products and careers by the start of the new year. And she’s not planning a version for men. “We are different, and creating Lulu really highlighted that. We need a place for just us to feel safe and speak our mind. I personally am not going to create a platform for men,” says Chong. “I don’t think we need the same things.”

The reason Lulu works is that it appeals to how women do their research on men before agreeing to a date. It answers questions early on, such as, is he career-motivated? Will he respect me? “A large portion of the conversations that women have are about relationships. Relationships are a really important topic to women, and we look to each other for advice on how to navigate that,” says Chong. “The majority of women will Google a guy before a date.”

Having some form of a “background check” if you will, is important to many women. Which is one reason why many are unsatisfied with rankings based solely on looks to determine sex appeal. If Lulu users rated Adam Levine based on what they know of him from the media, he might only get a 6. But we should remember that our evaluations of celebrities are more fantasies based on our own projections and online gossip, than reality. The real measure of Levine’s sex appeal would have to come from people who know him, for the rest of us he’s just eye candy.